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Stress–strain relationship of ductile materials and flexural behavior of ductile over-reinforced concrete beams

Duhaim Hussein M., Mashrei Mohammed A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2022

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Vol. 31, No. 4

225--237

EN

This paper aimed to investigate the effect of using ductile materials in the compression zone on the flexural performance of over-reinforced concrete beams. In order to avoid brittle compression failure, partial replacement of concrete with ductile materials layer in the compression zone was used. Four over-reinforced concrete beams of size 120 × 180 × 1,300 mm were cast and tested under three-point loading conditions. The steel fibers reinforced concrete (SFRC), slurry infiltrated fiber concrete (SIFCON), and ultra-high performance fiber reinforced concrete (UHPFRC) were used as ductile materials. The flexural capacity of the beams, failure modes, crack patterns, load-deflection relationships, ductility index, and toughness were investigated. The results showed that using ductile materials in the compression zone is an effective technique to increase the ultimate load, ductility, and toughness by up to 52.46, 84.78 and 279.93%, respectively, compared to the reference beam. In addition, the failure mode changed from brittle to ductile failure. Noting that the use of SFRC layer enhanced the ductility of over-reinforced concrete beams more than using UHPFRC and SIFCON layers. Also, one of the main advantages of this technique is led to increase the tensile reinforcement ratio up to 8.548% without needing the compressive reinforcement. Thus, ductile composite beams with a high flexural capacity were generated using an economical amount of ductile materials.

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The flexural behaviors and mechanism of wollastonite microfiber modified ultra-high performance concrete with steel fiber from micro to macro scale

Zeng Deming, Cao Mingli

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e32, 2022

EN

Wollastonite microfiber (WF) is a naturally occurring calcium silicate (CaSiO3) produced in fibrous form and often used in ceramic industry as a cheap and valuable mineral. It is tried to be applied in ultra-high performance concrete (UHPC) in this study with expectation to improve the flexural performance and compensate for the deficiencies of steel fiber in enhancing UHPC from micro scale. The effects of WF on the flexural behaviors of UHPC with or without steel fibers were explored. The bonding behaviors of steel fiber in WF-modified ultra-high performance concrete (WFMUHPC) under different curing conditions were researched combined with single fiber pull-out tests. The results showed that WFs could significantly resist and delay the formation of microcracks in UHPC. When WFs were added to UHPC with steel fiber, the flexural properties of concrete were significantly improved from micro to macro scale. Accelerated curing contributed to the flexural strengths but deteriorate the toughness of WFMUHPC with steel fiber. The presented load–deflection curves proved that WFs had a significant improvement of first crack load and there were post-peak curve gaps because of the reinforcing effect of WFs on the frictional sliding behavior of steel fiber. The results of X-ray diffraction and scanning electron microscope showed that WFs had the bridging and filling effect and improved the interfacial transition zone between WFs and matrix. Meanwhile, the combined effect between WFs and high temperature that WFs provided sites for hydration products from cement particles and active minerals including silica fume and fly ash further improved the flexural behaviors. Moreover, a flexural strength model established could accurately describe the reinforcing effect of WFs on this particular UHPC and was expected to provide guidance for practical engineering applications.

3

Flexural behavior of square hollow steel-reinforced concrete members

Ren Qingxin, Ding Jinan, Wang Qinghe, Liang Hui

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e34, 2022

EN

This paper presents an experimental investigation on the flexural behavior of the square hollow steel-reinforced concrete (HSRC) members. A total of six specimens with different hollow ratios and steel tube ratios were prepared, and their failure modes, strain distributions, the mid-span deflection, and bending moment were recorded. The obtained results showed that the HSRC specimen fails in a ductile mode and no local buckling occurs in the inner steel tube. The increase of steel tube ratio leads to the improvements of the ultimate bending moment, the flexural stiffness and the ductility coefficient. The ultimate bending moment can be increased by 52.8% when the steel tube ratio increases from 0 to 2.96%. To expand the ranges of parameters, a finite element model (FEM) was developed and benchmarked against the test results from this study. Then, a parametric study was conducted to quantify various influential factors on the flexural behavior of the square HSRC members, and the key influential factors were further determined. Based on the parametric investigation, a simplified design method on the prediction of the ultimate bending moment for the square HSRC members was provided to account for the contribution of the incompletely full-section yielded steel tube, and the predicted results from the simplified design method were satisfactorily in accordance with the experimental and numerical results.

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Experimental study on demountable steel ultra‑high performance concrete composite slabs under hogging moment

Guo Jun‑Yuan, Wang Jun‑Yan, Wang Yan-Bo, Gao Xiao‑Long, Bian Chen

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 3

art. no. e137

EN

Demountable steel-concrete composite structures have attracted much attention from researchers because of its fast construction, demountability and environmental friendliness. Using ultra-high performance concrete (UHPC) in the hogging moment regions of demountable steel-concrete composite structures might improve their crack resistance and flexural performance. In this study, the cracking behavior, failure mode, stiffness, ultimate strength and relative slip of demountable steel-UHPC composite slabs with different stud spacings and longitudinal reinforcement ratios under hogging moment were experimentally investigated. A welded steel-UHPC composite slab was also tested to compare its behavior with the demountable slabs. The test results show the demountable steel-UHPC composite slabs have excellent crack control ability under hogging moment due to the slip of threaded headed stud and the strain hardening behavior of UHPC; the relative slip is directly associated with the stud spacing and controlled by the friction and shear force of threaded headed studs. As compared to the welded composite slab, the demountable composite slab can be easily separated after loading, the flexural capacity is slightly smaller, while the crack control ability is better and the ductility is higher. A constitutive model considering the reduction of tensile strength of UHPC after reinforcement was adoptedl the design formulas were developed to predict the elastic limit and the ultimate moment, and the bending stiffness of the demountable composite slabs under hogging moment. The test results verify the applicability of the proposed constitutive model of UHPC and design formulas.

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Shear stresses of hollow lightweight concrete beams made with wood waste

Alharishawi Salam Salman Chiad, Rajaa Nagham, Shihab Lina Abdulsalam

Archives of Civil Engineering

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2021

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Vol. 67, nr 1

657--672

EN

Hollow Lightweight Concrete (HLC) beams are gaining popularity due to low cost and low weight as compared with the Solid Lightweight Concrete (SLC) beams. HLC and SLC beams decrease in weight, without losing strength and durability. Flexural and shear behavior of reinforced HLC and SLC beams made with sawdust under two-point load is investigated in this study. The ultimate deformation efficiency and shear resistant mechanism of HLC beams are discussed experimentally and compared with other SLC beams. The beams, tested in this research, are rectangular. Beams were designed and constructed as 12 * 23 * 100 cm. Six concrete beam models were prepared including three SLC beams without the hollow and the other three HLC beams poured hollow 50 * 7.5 cm throughout the all beam of 100 cm. All beams were split according to the distance between vertical stirrups, these stirrups were divided into three specimens 45, 13, and 6 cm. By analyzing six experimental test beams, in this research, investigated the effect of diverse factors on the shear of beams. On comparison with normal concrete beams, this work describes the failure of mechanism, process, and ductility. The first crack loads, ultimate loads, load-deflection behavior, crack patterns and shapes of failure were investigated in this study. The experimental results show the ultimate performance of HLC beams are pure shear and controlled by yielding tension and compression steel bars. Also, it is found that the measured size and configuration of the hollow opening had an effect on the load-carry capacity and mid-span deflection of HLC beams. Thus, the design and construction details of beams can be additionally customized to reduce the total cost and weight of the HLC beams.

6

Mechanical and thermal insulate behaviors of pultruded GFRP truss-core sandwich panels filled with EPS mortar

Li Sensen, Zhang Bei, Yang Dapeng, Wang He, Liu Yang, He Huguang, Fan Hualin

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

593--604

EN

Pultruded sandwich panel (PSP) usually has light weight, but its flexural performance is limited by the weak shear strength. Filling into expanded polystyrene (EPS) mortar can effectively improve the mechanical properties. The bending performance and failure mode of the EPS mortar-filled PSP were investigated by flexural testing. The ultimate bearing capacity improved from 49.562 kN for unfilled PSP to 72.065 kN for EPS mortar-filled PSP. The equivalent shear modulus is increased from 140.068 to 354.685 MPa. Increasing the EPS mortar’s density, the failure of EPS mortar-filled PSP would change from core shear failure, local indentation failure to overall shear failure. According to the thermal insulation tests, which shows EPS mortar-filled PSPs have excellent thermal insulation, the thermal insulation performance of different types of filler PSPs are obtained. The research on the mechanical and thermal insulation properties of EPS mortar-filled PSP can provide technical support for its application in engineering.